Using colony stimulating factors, culture techniques for long-term culture of normal hematopoietic cells have been established. Nontumorigenic bone marrow cells from NIH/Swiss, 129/J and C57BL/6 mice and spleen cells from NIH-Swiss, CBA and C57BL/6 mice have been maintained for over 12 months. Morphological and histochemical studies revealed that these cells are metachromatic cells capable of differentiation to basophilic granulocytes. These cells contain receptors for mouse IgE and histamine, which can be used as differentiation markers. Although these cells did not show colonies in spleens of lethally irradiated mice, colony and cluster formation was observed in methylcellulose medium, indicating that committed stem cells are maintained in suspension culture. These cell lines may be useful in studying the relationship between cell differentiation and viral oncogenesis.